1. Field of the Invention
The present invention relates to a method for measuring the free wire length in short-arc MIG/MAG welding by making use of the typical behavior of the current and the voltage in the bead short-circuit situation.
2. Description of the Prior Art
It is previously known to use the information obtained regarding the voltage and current of the electric arc for measuring the position of the welding burner. German Patent Application DE-OS 2 611 377 discloses a method in which the height of the welding burner is measured and adjusted by measuring the welding current. In the method the total current is measured. The disadvantage of the method is the dependence of the current on the wire feeding speed.
U.S. Pat. No. 4,169,224 describes a method in which the electric arc is compared with an electric analog. For this reason the use of the apparatus is limited primarily to the hot-arc range.
In U.S. Pat. No. 4,302,655 the position of the welding burner is measured by turning the burner so as to be perpendicular to the run direction and by measuring the variation of the welding current.
It is essential for the success of MIG welding that the so-called free wire length (l.sub.0) is of the desired magnitude. In manual welding the welder, on the basis of visual observation, makes sure that a suitable free wire length is maintained. In mechanized automatic welding the situation is different.
In automatic welding, the dimensional tolerances and unevenness of the pieces to be welded may produce a situation in which the current nozzle, guided in a predetermined manner, will not at all points remain at the correct distance from the workpiece.